Research On Geometric Error Identification And Compensation For Five-axis Machining Center

Error compensation is an important mean to improve the motion accuracy of five-axis machining center.At present,the geometric error analysis of the rotating axis of the five-axis machining center is not yet mature.And the existing error detection methods have the problems that the optical lens assembly is difficult to install and adjust its position,and the measurement time is longer.At the same time,the order of the polynomial also has an important influence on the accuracy of the error prediction model when the geometric error is parametrically modeled.Therefore,it is necessary to fully analyze the geometric errors of the five-axis machining center and improve the detection efficiency of geometric errors.Also,the prediction model that accurately reflects the error rule should be established.So that the geometric errors of the five-axis machining center can be accurately compensated.In this paper,the five-axis machining center is taken as the research object,focusing on error comprehensive modeling,error detection and identification,error parameter modeling and error compensation.The main contents are as follows:(1)The geometric error elements which affect the motion accuracy of the five-axis machining center are analyzed.The comprehensive modeling technology of geometric error is studied based on the theory of multi-body system.The transformation matrices of the workpiece coordinate system relative to the tool coordinate system under the ideal state and the actual state are respectively obtained by using the principle of homogeneous coordinate transformation.On the basis,the relationship between the position error of the actual cutting point relative to the ideal cutting point and the error elements is solved.And the integrated geometric error model of BC five-axis machining center is established.(2)The geometric error identification strategy of the moving axis and rotating axis is studied.The geometric errors of the translational and rotational axes are identified respectively by the nine-line method and six-circle method.The experiment of measuring the geometric error of the machining center is carried out.And all 41 geometric error elements are obtained by using the laser interferometer and the ball bar instrument.(3)A parametric modeling method based on Legendre polynomials is proposed according to the 41 measured geometric error elements.The modeling process is discussed in detail taking the positioning error of Y axis as an example.And the influence of different orders on the fitting accuracy is compared.The F-test method is proposed to determine the optimal polynomial order,and finally the relationship of all error elements on the coordinates of the moving axis is obtained.Combined with the geometric error integrated model,the position error of the actual cutting point relative to the ideal cutting point can be predicted according to the coordinate position of the tip point.(4)The coordinate position of the tip point is replaced by the geometric error model to calculate the error at the corresponding position.The NC program is modified to realize error compensation according to the predicted error value.The error compensation experiment under no-load condition and the milling experiment considering error compensation were carried out respectively to verify the compensation effect of the modeling and detection methods proposed in this paper on geometric errors.